GB2449114A

GB2449114A - Middle ear implant with piezoelectric actuator acting on stapes footplate

Info

Publication number: GB2449114A
Application number: GB0709072A
Authority: GB
Inventors: Eric William Abel; Robin Christopher Brodie; David Ernest Young
Original assignee: Sentient Medical Ltd
Current assignee: Sentient Medical Ltd
Priority date: 2007-05-11
Filing date: 2007-05-11
Publication date: 2008-11-12
Also published as: WO2008139225A2; GB0709072D0; WO2008139225A3; CA2724137C; CA2724137A1; US9686623B2; CN103442322A; JP5462151B2; EP2156702A2; US20120016180A1; JP2010526575A; EP2156702B1; CN101690266A; AU2008249763B2; CN101690266B; AU2008249763A1

Abstract

A middle ear implant 10 comprises a piezoelectric stack 12 as an actuator, piston means 14 joining a first end of the actuator to the stapes (stirrup) footplate 28, fixing means 16 attached to a second end of the actuator for securing the implant to an ossicle 26, a transducer for detecting sound, processor and amplifier means and a power supply. The stack and piston are coaxial and the fixing means is at right angles to their common axis. The piston means may extend around the piezoelectric stack and provide support for it. The actuator may be provided with a biocompatible coating that may also provide support for the structure. The ossicle to which the implant is attached may be the incus (anvil) long process.

Description

MIDDLE EAR IMPLANT

BACKGROUND TO THE PRESENT INVENTION

The present invention relates to devices for aiding the hearing impaired. More specifically the present invention relates to the provision of electromechanical actuators which can be directly attached to the ossicular chain of the middle ear for amplifying vibrations generated by sound signals.

Deafness affects 9 mIllion people in the United Kingdom, of which over 80% have Sensonneural Deafness (SD). This debilitating condition afflicts about 10% of the population of the western world. There are several causes and the ageing process is very important with a significant proportion of those affected being over 80 years old.

Hearing impairment is the third most common chronic problem affecting the ageing population -and one of the least diagnosed. There is also an increased prevalence in some sections of the younger age group, due to exposure to loud noise.

There are currently no effective means of repairing the cochlea or the nervous pathways to the brain. For most patients hearing can be restored adequately by sufficient amplification of sound with a hearing aid but middle ear implants (MEls) provide mechanical amplification by vibrating the ossicular chain and up to 50% of all people with moderate to severe sensonneural hearing loss could potentially be treated more effectively with these implantable devices.

Middle ear implants can utilise actuators in the form of electromechanical displacement devices, that control the position of a component through the use of an electric field. In this regard, piezoelectric actuators are known and are based on the piezoelectric effect, whereby certain crystalline materials exhibit the property of changing shape when subjected to an externally applied voltage. Most prior art piezoelectric actuators used in hearing augmentation systems require to be augmented by use in conjunction with one or more flextensional amplifiers and are often referred to as flextensional actuators.

Many types of piezoelectric actuator have been proposed, especially since the nineteen-fifties and, these are now described by those skilled in the art according to a series of classes defined by shape (Brigham and Royster, 1969). There were originally five classes but at least seven classes are now generally accepted. It is well known to those skilled in the art that minor changes in the design of actuators which may be generally similar in appearance can make highly significant differences to performance and even feasibility of use for a particular application.

Middle ear implants with actuators based on the use of piezoelectiic or electromagnetic transducers have been proposed. Actuators utilising piezoe(ect,ic transducers have the potential benefit of providing mechanical movement directly from an electrical signal to vibrate the ossicular chain as desired. Such actuators comprising piezoelectric transducers made from lead zirconate titanate (PZT) have been used in different configurations to provide assistance to the hearing impaired.

In US Patent No. 6,629,922 to Puria at al the authors describe a flexextensional actuator for surgically implantable hearing aids wherein a piezo element is disposed between two end caps which function as flextensional amplifiers and these three components are glued together with suitable adhesive means. The authors refer to the actuator as a pnsmatoid type, however, it conforms with the widely accepted description of a cymbal actuator; a point which is conceded in several parts of the description, for example, with respect to their Fig. 4F. The authors contemplate encasing the actuator in biocompatible material to isolate it from the body.

In published PCT Application WO 20061075169, the authors describe an actuator having a multi-layer piezo-etectjic stack and a frame component comprising at least one flextensionaj amplifier element and also having integral first and second end portions integral with and disposed substantially at right angles to the main plane of the flextensional amplifier or amplifiers.

The present authors have been unable to find any examples in the prior art of middle ear implants having actuators comprising a piezoelectric stack of this type and attachment means for attaching the actuator to the ossicular chain but having no flexextensional elements.

OUTLINE OF ThE PRESENT INVENTION According to a first aspect of the present invention there is provided a middle ear implant in the form of an actuator for an implantable heaiing aid system comprising a stack of up to about 50 ceramic piezoelect,jc elements each of approximately 0.04 sq mm and preferably made from lead zirconate titanate (PZT) and arranged in d33 configuration.

This actuator, when used alone, driven by a relatively high (given the application) 5V input voltage, is capable of producing levels of amplification which match or exceed those achieved with prior art actuators provided with cap or frame flexextensionat amplifiers.

According to a second aspect of the present invention, the actuator of the first aspect is provided with attachment means for attachment to an osside of the ossicular chain, specifically the incus long process. Attachment means are preferably in the form of dip means designed to provide constant loading means on the incus such that applied loads do not reach the level at which necrosis is induced. Such a clip may be constructed from alloys such as nhtinol according to designs which take account of the superelastic property of that material. The clip attachment means may be fixedly attached to the actuator by adhesive means.

According to a third aspect of the present invention there is provided a piston, fixedly attached to the actuator and of such a length that, at implantation, it is brought into gentle pressing contact with the stapes footplate. Fixed attachment of the piston to the actuator may be achieved by the use of adhesive means and it Is highly preferable that the long axis of the piston and the long axis of the actuator stack are substantially coaxial. Furthermore ft is also highly preferable that the dip is secured such that the effective axis of operation and the gape of the jaws thereof are arranged substantially at nght angles to the shared axis of the actuator and piston. The piston may be made from any one of a number of materials including, non-exclusively, titanium, Teflon"', gold or nitinol and its length may be adjusted intra-operafively if required. When suitable metals or alloys are used to construct the piston it may be extended to provide containment means for the actuator and boss means for the clip. It is also possible when suitable matenals are selected, to form the clip integrally with the piston, containment means for the actuator and boss.

Such an arrangement comprising these three aspects of the present invention has not been disclosed either in the prior art patent literature nor in the medical or scientific literature relating to middle ear implants or hearing augmentation in general.

According to a fourth aspect of the present invention there is provided a Sound transducer, convenienny in the form of a microphone, which may be located for instance externally in the ear canal or behind the plnna, or internally by implanting it in the pinna or such other site as the surgeon may select.

According to a fifth aspect of the present invention there is provided a sound processor, preferably a digital signal processor (DSP), which may conveniently, but not necessarily, be located with or in close association to the sound transducer to which it is hard wired or wirelessjy connected and from which it derives Its input signal. The DSP is preferably able to condition sound information contained in the signals detected by the transducer (microphone) such that the profile of hearing loss in each patient may be precisely compensated for at different parts of the hearing spectrum.

According to a sixth aspect of the present invention there is provided a power supply, conveniently a battery, which may be located for Instance externally in the ear canal or behind the pinna, or internally by implanting ft in the pinna or such other site as the surgeon may select. The power supply provides power to the DSP and, where appropriate, to suitable amplifier means and is Preferably hard wired to both of these components. Power supply selection may be from an expendable battery if mounted externally or a very long life implantable battery using technology employed in pacemaker batteries or a rechargeable battery such as an induction coil chargeable device.

According to a seventh aspect of the present invention wires are used to connect the electrical components together. Preferably these are very fine and are provided with biocompatible coatings or sheathings. Certain portions of the wiring may pass transcutaneously, subcutaneously or within a bony canal between components.

According to an eighth aspect of the present invention, the middle ear implant components which are to be implanted are secured together with suitable adhesive means. it is also necessary to isolate the implantable components from their immediate local environment and this is conveniently achieved by coating with a material such as ParyleneTM. Where appropriate, encapsulation coating means which also constitute adhesive means may be used to secure implantable components together as well as to isolate them from their local environment

BRIEF DESCRIPTION OF ThE DRAWINGS

Further preferred features and advantages of the present invention will appear from the following detailed description of some embodiments illustrated with reference to the accompanying drawings in which: Fig. I is a schematic right lateral view of an actuator according to a first preferred embodiment of the present invention comprising a piezo&ectric component having a stack of piezoelectric elements, a piston element and connecting means for attachment to the ossicular chain of a human or animal patient.

FIg 2 is a schematic posterior view of the actuator of Fig I. FIg. 3 is a schematic left lateral view of an actuator according to a second preferred embodiment of the present invention comprising a piezoelectric component having a stack of piezoelectric elements, a piston element and connecting means for attachment to the ossicular chain of a human or animal patient wherein extensions of the piston and ossicular attachment means constitute support means substantially surrounding two sides of the piezoelectric component.

Fig 4 is a schematic posterior view of the actuator of Fig 3.

FIg 5 is a schematic perspective view of the actuator of Fig 3.

Fig. 6 is a schematic left lateral view of a modified version of the actuator of FIg. 3, comprising a piezoeiecfjic component having a stack of piezoelectric elements, a piston element and connecting means for attachment to the ossicular chain of a.uman or animal patient wherein extensions of the piston and ossicular attachment means constitute side support means substantially sUrrounding two sides of the piezoelectric component, the side support means being provided with locally modified areas.

Fig. 7 is a schematic right lateral view of an actuator according to a third preferred embodiment of the present invention comprising a plezoelectric component having a stack of piezoelectric elements, a piston element and connecting means for attachment to the ossicular chain of a human or animal patient wherein a coating of the piston, attachment means and piezoelectjjc component substantially surrOunds the entire actuator and thereby providing support means.

Fig 8 is a schematic posterior view of the actuator of Fig 7.

Fig 9 is a schematic perspective view of the actuator of Fig 7.

FIg 10 is a schematic view of the actuator of FIg 7, shown located within the ear of a human patient; FIg 11 is a schematic front view of a series of moulded plastic trials for an actuator according to the present invention indicating varying piston lengths.

Ag 12 is a schematic diagram of the main components of an implantable hearing aid system suppocting use of a middle ear implant actuator according to the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

With general reference to Figs I -12, reference is first made to FIgs. 1 and 2, in WhiCh there is shown an actuator 10, for a middle ear implant according to a first preferred embodiment in accordance with aspects of the present invention.

A middle ear implant is in the form of an electromechanical actuator 10, which comprises a piezoelectric stack 12, desirably having about 50 piezoelectiic elements advantageously about 0.4 mm by 0.9 mm in cross section and each of about 0.1 mm thickness, preferably made from lead zirconate titanate (PZT) and arranged in d33 configuration and indicated by way of example at 12a, 12b, 12c and 12d. A piston element 14, is disposed such that the long axes of 12, and of 14, are substantially coaxial and connecting means for attachment to the ossicular chain of a human or animal patient Which are in the form of an open jaw clip 16, the gape' or entry 16a, of which is arranged substantially at right angles to the coaxial arrangement of 12, and 14.

Piston 14, and open jaw dip 16, may be made, conveniently, in suitable materials such as titanium, gold, nitiriol, plastics or any other suitable material Proximal end 18, of 12, is fixedly attached to dip 16, by adhesive means indicated at 20. and which may conveniently be an acrylic polymer. Distal end 22, of 12, is fixedly attached to piston 14, by adhesive means indicated at 24, and which may also conveniently be an acrylic polymer.

it is to be noted that, although the instant invention is herein described with reference to a piezoelectric stack 10, WhiCh is oblong in plan view 10, may equally readily be square, or round, or any other convenient shape in plan view.

As may be seen by brief reference to Fig 10, in use, clip 16, is attached to an ossicle, typically the incus long process 26, and actuator 10, is disposed in such a way that piston 14, is brought to bear gently but firmly on the stapes footplate 28, or in a hole formed therein (not illustrated) by surgical intervention. Actuator 10 may be provided in a series of sizes wherein piston 14 has a different length for each size. Size selection may be assisted by comparison with a series of simple plastic trials' described hereinafter with reference to FIg 11. Alternatively, an over-length piston may be selected and reduced to an appropriate length intra-operatively.

Experiments using a bench rig have shown that when actuator 10, is driven at approximately 5 volts, d33 axial excursions of stack 12, measured with a Polytec laser vibrometer can exceed 40 nanometres equivalent to sound pressure levels (SPL) considerably in excess of 100 dB.

Experiments using human cadaveric temporal bones have confirmed that when actuator 10, is driven as immediately hereinbefore described, vibration measurements at the stapes footplate similarly equate to an SPL over 90 dB.

Reference is now made to Figs. 3 -6, in which there is shown an actuator 110, for a hearing aid system according to a second preferred embodiment in accordance with aspects of the present invention.

Actuator 110, comprises a piezoelectric stack 112, having about 50 piezoelectric elements and indicated by way of example at 112a, 112b, 112c and 112d, preferably made from lead zirconate titanate (PZT) and arranged in d33 configuration. A piston element 114, is disposed such that the long axes of 112, and of 114, are substantially coaxial. Connecting means for attachment to the ossicular chain of a human or animal patient are in the form of an open jaw clip 116. the gape' or entry 116a, of which is arranged substantially at right angles to the coaxial arrangement of 112, and 114.

Base portion 150, of open jaw clip 116, extends along the whole of first edge 152, of stack 112, and also along the whole of third edge 154, of stack 112, forming first and second stde supports 156 and 158, respectively. At the distal end 160, of stack 112, first and second side supports 156; 158, extend continuously into proximal end 182, of piston 114. It will be appreciated that open jaw clip 116, base portion 150, first and second side supports 156; 158, proximal end 162 and piston 114, constitute a single structural entity and may be made in materials such as titanium, gold, nitinol, plastics or any other

suitable material.

It is to be understood that the function of first and second side supports 156; 158 is exactly as the name implies and that they have no possibility of functioning as fiextensional amplifiers. Their presence may be desirable because, when actuators 10, 110, of embodiments of the present invention are driven at the design voltage of 5 volts, excursions of stack 12, of Figs I and 2, and stack 112, of FIgs 3-6, may be measured in several tens of nanometres and the provision of first and second side supports 156; 158 contributes significantly to longevity and reliability, both of which are extremely important factors in implanted medical devices.

Nitinol, certain plastics and, to some extent gold, have an inherent capacity for non-plastic deformation and recovery when stressed in the cyclical manner associated with piezoelectric stacks.

It is also to be noted that, although the instant invention is herein described with reference to a piezoelectric stack 10; 110, which is oblong in plan view 10; 110. may equally readily be square, or round, or any other convenient shape in plan view. In any evert the disposition of first and second side supports 156; 158, is preferably on opposite sides of stack 112.

Fig 6,is a variant of the embodiment of the actuator of FIgs 3-5, wherein side supports 156; 158, have local modified areas 164; 166 extending transversely preferably, though not necessarily, at their respective mid points 168; 170. The form of locally modified areas 164; 166 in cross section is such that substantially triangular shaped zones are enclosed between side supports 156; 158, and respective first and third edges 152; 154 of stack 112. Areas 164; 166 are so arranged as to provide substantially unrestricted excursions of actuator 110, in response to amplitudes which are functionally useful in providing hearing augmentation but also providing excursion limiting or attenuating means in the event of very large excursions which might occur in response to high energy signals, such as transient Sound signals, in conjunction with the high driving voltage of the device.

FIgs. 7-9 illustrate an actuator 210, according to a third preferred embodiment of the present invention comprising a piezoelectric stack 212. a piston element 214, and connecting means comprising clip means 216, for attachment to the ossicular chain of a human or animal patient Elements 212, 214 and 216, are seen in outline only by virtue of a coating 272, which substantially surrounds the entire actuator 210, including stack 212, piston element 214, and clip 216 Although 272, has some resilience, it is sufficiently stiff and has sufficient strength and structural integrity to provide support means on all four sides of 212, indicated in outline at first and th'rd edges 252; 254, and also second edge 252a, and the fourth edge which is not seen.

The proximal end of stack 212, is fixedly attached to dip 216, by adhesive means (not seen) which may conveniently be an acrylic polymer. The distal end of 212, is fixedly attached to piston 214, by adhesive means (not seen) which may also conveniently be an acrylic polymer.

Coating 272, may be made of the same material as adhesive means used to secure piston 214, and dip 216, to stack 212, or may be made of a different material, in any event is it important that coating 272, is made from biocompatible material.

It is further to be noted that, although the instant invention is herein described with reference to a piezoelectric stack 210, WhiCh Is oblong in plan view, 210 may equally readily be square, or round, or any other convenient shape in plan view.

Note that coating 272, is not the direct equivalent of a proprietary coating used for shielding surgical implant materials from biohazards, rather it is a structural component However, it is highly desirable that a btocompatible ultra thin layer outer layer of a material such as Parylene is used to protect the body from the implant and vice versa from toxic or other undesirable agents.

All three embodiments of the present invention immediately hereinbefore described are deployed at surgery in substantially the same manner by introducing the gape 16a; 116a; 216a of dip 16; 116; 216, respectively, to the incus long process and gently pushing it to cause opening and subsequent engagement, location and dosing of dip 16; 116; 216. This procedure may be aided by using a suitable instrument to gently prise open the clip 16, 116, 216. However, it is to be understood, by non-surgeons and surgeons alike, that the entire device 10, 110, 210 is extremely small, measuring usually no more than 5.5 mm in length (and generally less) and concomitantly clip 16, 116, 216 is designed to surround an ossicle of ovoid cross section likely to be no more than 0.7 mm in one direction and 0.9 mm In a second direction and will inevitably be extremely small and delicate, no matter from what material it may be made. Reference to FIg 10, shows the middle ear implant in situ in the ear of a patient.

Pistons 14; 114; 214 may require to be provided in differing lengths for different patients whose anatomy varies in a more or less known but unpredictable (pre-surgery) basis.

Accordingly, a supplier supplying a surgeon user with actuators 10; 110; 210, in different lengths may assist by also supplying trials 80, as illustrated in Fig 11. Trials 80, are conveniently moulded in suitable plastics by injection moulding and are supplied stenlised. Trials 80, comprises representations indicated at 82, 84, 86, 88, 90, 92, 94, in moulded plastics of all available sizes of actuator 10; 110; 210, in the suppliers exemplary range, each size being clearly indicated, for example by being provided with numerical information moulded into the body of trials 80, as exemplified at 96, and secured by a very small breakable tag indicated at 98. At surgery, and with the target site exposed and prepared, tnals 80, is removed from its sterile packaging, usually by an assistant to the surgeon and a selected size is grasped in small surgical tweezers, wrested free from tag 96, and carefully offered up to the surgical site to establish the appropriateness of that size or otherwise, by a relatively swift process of trial and error, the optimum size of 10:110; 210, may be selected and implanted.

Under an alternative regime, piston 14; 114; 214, may be deliberately selected over-length and trimmed down to the required size intra-operatively.

Referring to Fig 12, there is illustrated, in schematic form, a suitable arrangement for use of the middle ear prosthesis of the present invention, specifically mechanical actuator 10; 110; 210, in a partially implantable hearing aid system 11. Microphone 13, may conveniently be situated in the ear canal 15, and its output directed by connecting wires, generally indicated at 17; ha, to a DSP which, together with appropriate ancillary circuitry, is indicated at 19, and an amplifier 21, located in a housing 23, and which may conveniently be placed behind the ear 25, of a patient Housing 23, (shown out of its in-use resting position for clarity) also conveniently provides housing means for at least one battery 27. Battery 27, provides power to DSP and circuitry 19, amplifier 21, and to stack 12; 112; 212, of actuator 10; 110; 210, respectively. Electrical connection conveying output from DSP and circuitry 19, and amplifIer 21, to stack 12; 112; 212, of actuator 10; 110; 210. is achieved using connecting wires 17; fla, which are run in a surgically created tunnel indicated diagrammatically at 29, extending medially from a point dose to the superior origin of the pinna 31, subcutaneously and where appropriate (L1 sub-periosteally and trans-osteally to a point within the middle ear space 33, slightly anterior of the lateral aspect of the malleus from whence 17: ha emerge, thereafter extending to conned with stack 12; 112; 212.

DSP 19, may be operated at up to 2.5 volts DC or more, depending upon its type and model and battery 27 is selected so as to provide this. DSP 19, is a commercially available device such as the Orela 4505 from AMI Semiconductor SA (Louvain, Belgium) which is provided with a voltage doubling feature. The output from 19, may be input to amplifIer 21, and the output from 21, conveniently employed to drive actuator 10; 110; 210.

Although actuator 10; 110; 210, is generally a very low current consumption device, the current requirement is frequency dependent so the voltage doubling feature of DSP 19, may be inadequate at higher frequencies. A suitable alternative would be to use a charge pump attenuator using a 5 volt battery, attenuating to 2.5 volts for powering DSP 19, and 5 volts to supply power amplifier 21.

Although several preferred embodiments of the present invention have been described in the foregoing detailed description, it is to be understood that the invention is not limited to those embodiments disclosed herein but is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the invention as set forth and defined by the following claims:

Claims

A middle ear implant for implantation in the middle ear of humans and animals in the form of an electromechanical actuator comprising: Actuator means in the form of piezoelectsic stack means Piston means fixedly attached to the distal end of said piezoefectric stack means constituting engagement means for the stapes footplate Ossicle attachment means fixedly attached to the proximal end of said piezoelectric stack means for the attachment of said prosthesis to an osside Transducer means for detecting sound information Sound processor means and amplifier means for processing sound information detected by said transducer Power supply means for supplying power to drive said actuator, said sound processor and said amplifier and Connecting wires to connect the components wherein Said piezoetecthc stack means are disposed between said piston means and said ossicle attachment means such that said stack and said piston means are substantially coaxial and said coaxial arrangement is substantially at right angles to the line of operation of said ossicle attachment means; and said actuator, said sound processor, said amplifier, said transducer and said power supply are connected by said connecting wires in such a manner as to power said sound processor and said amplifier and to drive said actuator with sound information detected by said transducer such that said actuator is caused to vibrate at frequencies substantially the same as those detected by the transducer and said ossicle and said stapes footplate are in consequence also caused to vibrate at frequencies substantially the same as those detected by the transducer and with increased amplitude;
2. A middle ear implant according to Claim 1, wherein said piston means extend about first and second ends of said piezoelectric stack and also around at least two aides thereof constituting first and second side support means for said stack further extending in a continuous manner Into said ossicle attachment means;
3. A middle ear implant according to Claim 2, wherein said first and second side support means have first and second locally modified areas;
4. A middle ear implant according to Claims I to 3, wherein said actuator is covered overall with coating means having sufficient structural strength and integrity to constitute side support means on alt four sides;
5. A middle ear implant according to Claims I to 3, wherein said actuator is covered overall with thin biocompatible coating means constituting ingress prevention means for organisms and detritus and egress prevention means for organisms and chemicals from said stack and its constituent parts.